Method for manufacturing a multi-layered pulp product comprising a filler between layers

ABSTRACT

The present invention refers to a procedure for the manufacture of a multi-layer pulp product, preferably paper or cardboard. Said procedure consists of applying a filler between at least two layers of fibre material in motion prior to the final joining together of them. The filler is preferably of inorganic origin, though it can consist of organic components, and calcium sulphate is preferably used.

RELATED APPLICATIONS

[0001] The present application is a Continuation of co-pending PCTApplication No. PCT/ES01/00234, filed Jun. 6, 2001. Applicants claim thebenefits of 35 U.S.C. §120 as to the PCT application, and the entiredisclosure of the application is incorporated herein by reference in itsentirety.

TECHNICAL FIELD OF THE INVENTION

[0002] The present invention refers to a procedure for the manufactureof a multi-layer pulp product, in particular a product selected frombetween paper and cardboard and which presents the essentialcharacteristic of incorporating a filler between layers.

BACKGROUND OF THE INVENTION

[0003] Many products such as paper and cardboard are constituted by thesuperposition of layers of fibres which can be of the same type or ofdifferent qualities. In multi-layer pulp products the outer layers whichgrant that paper or cardboard its final appearance are distinguishedfrom the inner layers, which can be constituted by virgin paste,recycled paste or mixtures of the two. In general, the inner layers havea dark colour which sometimes needs to be masked with the outer layers,for which one or several layers of white fibres (virgin or recycled) areusually added, with a layer of pigment being able to be applied to thesurface afterwards.

[0004] In the manufacture of products such as paper or cardboard, thefillers are of vital importance since by means of them a saving can beachieved in the amount of virgin or recycled fibre that is used. Theobject of adding fillers during manufacture is also to improve oracquire certain properties that are desired in the end product:improvement in optical properties such as whiteness, opacity, brightnessand colour; improvement in properties relating to permeability tofluids, such as penetration of water or ink, penetration of oil andporosity or resistance to the passage of air. The addition of fillers tothe paper also permits the speed of the machine to be increased, whichimproves its production.

[0005] Independently of whether the type of machine for the manufactureof paper or cardboard is a Fourdrinier machine—flat table—or a cylindermachine, or a combination of the two, different ways of introducingfillers into the paper are described in the art.

[0006] International application WO-9600816 describes a method and adevice for applying a film of a coating material on a network or tissueof fibres in a paper or cardboard machine. The coating material isapplied on the surface of the mesh of the pulp product by means of aspraying system at low pressure and high flow. The system is equippedwith a series of spray guns adjacent to the mesh of the pulp product.Nevertheless, this procedure is solely intended for the manufacture ofmono-layer paper. The mono-layer paper coating thus described has thedrawback that it is complicated to achieve a correct distribution of thefiller over the entire section of the paper since the penetration of thefiller within the fibre mesh will vary radically depending on the pointof application.

[0007] The application for European patent EP-0 373 276-A1 describes aprocedure and device for the continual spraying of adjuvants on apermeable fibre mesh arranged on a belt which is displaced. The systempermits spraying of the adjuvants in different states of humidity of thesheet undergoing formation by means of one or various spraying ramps.Each of them is supported by a movable support frame transverselyarranged in relation to the direction of displacement of the belt. Thisramp is constituted by two ducts provided with nozzles for the transportof the adjuvants, with starch being the product that is sprayed andwhich penetrates throughout the entire thickness of the sheet.

[0008] In spite of the above examples, known techniques for introducingfillers into the interior of the fibre mass present drawbacks such asthe low transference of that filler, with a major loss of raw materialstaking place which has repercussions on the manufacturing costs. Anotherdrawback consists of the reduction in the mechanical properties of thepaper, which become more important as the content of filler increases.

[0009] It is therefore necessary to be able to have a procedure withwhich the transference of filler to the paper manages to be increased,which will also improve its optical properties (whiteness, opacity,etc.) and which does not lead to any major reduction in mechanicalproperties. All these factors will result in an overall improvement ofthe manufacturing process.

[0010] In the case of multi-layer paper, the above objectives can beachieved by means of the manufacturing procedure of the presentinvention. This procedure is innovative since, among the knowntechniques for the manufacture of multi-layer paper, no description hasyet been made of the application of a filler between layers of fibre(which can be of different compositions and can contain differentadditives), and which acquire the filler prior to being joined together.

OBJECT OF THE INVENTION

[0011] The present invention refers to a procedure for the manufactureof a multi-layer pulp product. Said procedure essentially consists ofapplying a filler between at least two layers of fibre material inmotion prior to the final joining of them together.

DESCRIPTION OF THE INVENTION

[0012] The present invention refers to a procedure for the manufactureof a multi-layer pulp product, characterised in that it consists of:

[0013] the continuous exit of fibre material from one or more entranceboxes of a pulp product manufacturing machine,

[0014] the depositing of said fibre material on one or several sectionsof the pulp product manufacturing machine, obtaining one or severalmoving fibre meshes and forming different layers of the fibre materialin one or several layer formation sections,

[0015] the draining of those layers during their trajectory on the layerformation, section,

[0016] the introduction of filler, by certain application means, betweenthe layers of said fibre material which is being displaced via aconveying means, and

[0017] the joining together of those layers.

[0018] The position of the one or more application means with respect tothe layer formation section of fibre material can be variable. Thefillers can be proportioned by the application means on one or anotherlayer.

[0019] The introduction of filler is done at a distance of between 1 and70 cm above the moving fibre mesh and preferably between 5 and 40 cm.

[0020] The fillers used in the procedure of the present invention areapplied by one or several means which are transversely located on themoving fibre mesh, with those application means being arranged in one orseveral series at different distances from the entrance box for the pulpproduct manufacturing machine.

[0021] The means of filler application can also be arranged with anangle of inclination with respect to the plane of the moving fibre meshof between 0 and 90 degrees, this angle preferably being 25 degrees.

[0022] The final configuration of the application system essentiallydepends on the speed and configuration of the pulp product manufacturingmachine.

[0023] According to the procedure of the present invention, theapplication means of the filler are located in a transverse directionwith respect to the direction of displacement of the moving belt. Theapplication of filler can be done by various application means, beingable to be introduced in a single application or in successive layers offiller.

[0024] The means of filler application preferably consist of nozzles,the filler being applied by spraying of a suspension of the fillerbetween layers of pulp material (the moving fibre mesh is displaced at aspeed between 50 and 2000 metres a minute).

[0025] The use of nozzles permits the introduction of filler accordingto a shape selected from between jets of conical shape and plane jetswith variable angles of opening, preferably 60°.

[0026] The spraying can be done by means of a system that includesnozzles and a return, which provides effective control of the flow orstream in the nozzles. The flow in the nozzles can be adjusted bycontrol means and the said return. The control means are preferablyselected from between a pressure regulator, a flow regulator and a pumpfitted with a frequency shifter.

[0027] The filler is introduced with a transference efficiency ofgreater than 70%, preferably between 90% and 100%.

[0028] The filler can penetrate into the interior of the moving fibremesh with a depth that is determined by the distance of the applicationmeans of the filler with respect to the entrance box. The filler ispreferably sprayed at the end of the formation of the sheet at adistance from the entrance box that guarantees little penetration (inorder to achieve the best coating of the inner layers).

[0029] The manufacturing machine for the product is preferably a paperor cardboard machine, and the multi-layer pulp product is paper orcardboard.

[0030] The procedure of the present invention can be carried out in anykind of paper or cardboard machine, so said machine can be a Fourdriniertype of machine, a cylindrical machine or a machine which is acombination of both.

[0031] The filler is preferably of inorganic origin, though it caninclude organic components.

[0032] Among fillers of inorganic origin in the procedure of the presentinvention, use is preferably made of calcium sulphate, calciumcarbonate, titanium dioxide, talc, kaolin, alumina trihydrate or amixture of two or more of these components.

[0033] The carbonate can be selected from between a natural calciumcarbonate or a precipitated calcium carbonate.

[0034] In an especially preferred embodiment of the procedure of thepresent invention, the filler that is used is an anhydrous calciumsulphate of high whiteness.

[0035] The calcium sulphate is selected from:

[0036] natural anhydrous calcium sulphate,

[0037] anhydrous calcium sulphate coming from chemical synthesis, and.

[0038] anhydrous calcium sulphate obtained by dehydration of a calciumsulphate selected from:

[0039] natural calcium sulphate hemihydrate,

[0040] natural calcium sulphate dihydrate,

[0041] calcium sulphate dihydrate coming from chemical synthesis, and

[0042] calcium sulphate hemihydrate coming from chemical synthesis.

[0043] The calcium sulphate is preferably dispersed in water (by meansof vigorous stirring) in proportions of up to 60% by weight in relationto the total mass of the suspension. The granulometry of the filler isalso an important factor for the procedure of the invention. The finegranulometry, coating power and high refractive index of calciumsulphate improve the opacifying capacity of the white layer.

[0044] The calcium sulphate used in the invention has a meangranulometry of between 0.5 and 50 μm. The filler preferably has aparticle size lying between 0.5 and 10 μm. The filler can include adispersant in a proportion between 0.01% and 1% of the weight of dryfiller.

[0045] The filler is applied as an aqueous suspension, the quantities ofwater and filler being controlled preferably by weighing. Also, saidfiller is applied by generally controlling the stream by means of a flowregulator and/or by means of a pressure controller.

[0046] The rheological properties of calcium sulphate enable a widerange of dry extracts to be worked with, and the optimum quantity offiller between layers can thus be determined for each type of quality tobe manufactured.

[0047] In a preferred embodiment the filler is applied as an aqueoussuspension consisting of between 99% and 40% of water. It preferablyconsists of between 90% and 70% of water.

[0048] The quantity of filler deposited on the fibre mesh lies between0.5 g/m² and 50 g/m², and very preferably between 5 g/m² and 15 g/m².

[0049] The filler can optionally include one or more additives. Forexample, it can include various types of starches or mixtures of them.

[0050] The fibrous material constituting the multi-layer pulp productproduced by the procedure of the present invention can be constituted bya paste selected from among virgin paste, recycled paste, paste that hasbeen de-inked or not, all kinds of paste whitened or not, and mixturesof the above.

[0051] The present invention has as an additional object a paper orcardboard product produced according to the described procedure.

[0052] The advantages obtained with the procedure of the presentinvention are multiple:

[0053] A saving in filler is achieved owing to filler retentions ofhigher than 70% being attained without the use of outside chemicalagents.

[0054] Another additional advantage of the procedure of the presentinvention is that it permits inner and outer layers of the end productto be of inferior quality, thus considerably reducing the cost of theend product. If the same quality is maintained for the inner and outerlayers, then the application of filler between layers permits an endproduct to be obtained that has a better overall quality.

[0055] Another additional advantage of the procedure of the presentinvention is that the white prelayer or prelayers (if the end product isconstituted by several outer white layers) can be replaced, with thedesired optical properties being maintained.

[0056] Another additional advantage of the procedure of the presentinvention is that it also permits a reduction in the grammage of thewhite layer, maintaining the desired optical properties of the endproduct, thereby considerably reducing the cost of the manufacturedproduct.

[0057] Another additional advantage of the procedure of the presentinvention is that by means of using calcium sulphate an improvement inthe efficiency and homogeneity of the coating between layers isachieved.

[0058] The following figures and example show in a more detailed mannercertain aspects of the invention.

BRIEF DESCRIPTION OF THE FIGURES

[0059]FIG. 1 show a series of positions of a device conceived for theintroduction of fillers according to the procedure of the invention andsuitable for different configurations of machine. In that figure:

[0060]1 represents an application means of filler,

[0061] (a) shows a section of a combination of Fourdrinier machines andcylindrical machines,

[0062] (b) shows a section of a combination of cylindrical machines, and

[0063] (c) shows a section of combination of Fourdrinier machines.

[0064]FIG. 2 shows a system of introducing filler by spraying, saidsystem consisting of a series of nozzles permitting the suspension offiller to be sprayed in jets with a conical or plane shape. Representedin that figure is a jet with a plane shape 2 or conical shape 3.

[0065]FIG. 3 shows a possible configuration of the application means offiller with respect to the moving fibre mesh. In that figure:

[0066] “h” represents the distance between the means of application andthe surface of the fibre mesh

[0067]4 represents the sprayed filler

[0068]5 represents the pulp product and

[0069]6 represents the support for the moving pulp product (fabric)

[0070]FIG. 4 shows a diagram of the preparation, storage and spraying offiller in the form of suspension. In that FIG. 4 can be seen a sectionof storage of the filler 7, a section of dilution of the preparation 8,a section of storage of the filler suspension 9, a sprinkling system 10which includes a final batch 10 a, and a section of the device for theintroduction of filler between the layers of pulp product 10 b.

[0071]FIG. 5 shows the section or sprinkling system 10 of FIG. 4. It isa standard diagram of the introduction of filler in the form ofsuspension. In FIG. 5 can be seen a filler filter 11, the flow controlpoint 12, the positions of the flow meters 12 a and 12 b, and thesection of the filler spraying ramp 13 between the pulp product layers.

[0072] This system can be subject to specific modifications permittingboth the elimination or addition of elements and the modification bymeans of other more sophisticated components.

DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

[0073] Described below is the use of the present invention in themanufacture of multi-layer paper, specifically white Biclass.

[0074] Provided on a conveyor belt of a Fourdrinier type paper machinebeing displaced at 142 m/s is a mesh of cellulose fibres coming fromrecycled white paper. At a distance of 40 cm (h in FIG. 3) above thesurface of the fibre mesh a filler spraying system is provided, having14 nozzles like those shown in FIG. 2. The angle of inclination α—asshown in FIG. 3—of the nozzles with respect to the moving fibre mesh is25°.

[0075] By means of an installation similar to that described in FIG. 4and under conditions of vigorous stirring, a 25% aqueous suspension isprepared of anhydrous calcium sulphate (coming from the dehydration ofcalcium sulphate dihydrate) with an average particle size of 3 μm. Thequantities of water and filler are controlled by weighing. By means ofthe spraying system described in the above figure, 17 g/m² of anhydrouscalcium sulphate are proportioned on the surface of the moving paper(10% by weight on the white layer production). The flow of filler iscontrolled by means of an automatic flow regulator, the spraying pointbeing located at the end part of the formation table and after the waterline. At the end of the formation table the joining of the white layerwith the grey support takes place.

[0076] In this way, a 90% transference of filler takes place, and a veryconsiderable increase in the whiteness of the outer white layer of thepaper can be observed.

[0077] The results obtained by the application means of anhydrouscalcium sulphate in the interlayer following the procedure describedabove were compared with the results obtained using kaolin as filler inthe mass of the white layer. The conclusions of the comparison are asfollows:

[0078] For an objective whiteness value of 77, the grammage of the whitelayer was reduced from 81 to 65 g/m², with the consequent economicsaving.

[0079] For the same value of grammage of the white layer (81 g/m²) andmaintaining the same mechanical properties as were achieved with kaolin,it was possible to increase the percentage of ash from 18% to 23% bymeans of spraying with calcium sulphate.

[0080] The transference of filler went from 40% for kaolin to 90% forcalcium sulphate. The spraying with calcium sulphate avoided the use ofthe retention agents needed in the case of kaolin.

[0081] The values of delaminating and of “Dennison” waxes remainedsimilar at all times 0.199 joules/m² (95 ft.lb/in²) and 0.01892joules/m² (9 ft.lb/in²) respectively, for the two cases.

[0082] As calcium sulphate is a filler with superior whiteness andopacity characteristics to the kaolin used in the mass, this permittedthe use of recycled paper of poorer quality (and therefore much moreeconomical). Using kaolin, recycled white paper with a minimum whitenessof 75.5 had to be used, while with calcium sulphate it was possible toreduce this whiteness to 72.5.

[0083] The whiteness of the final paper by means of spraying withcalcium sulphate between layers increased potentially as a function ofthe percentage of filler applied.

[0084] Having illustrated and described the principles of the inventionand its application to a particular case, it can be appreciated that itis in no way limited to the example presented here. Numerousmodifications can be made to the method and the apparatus in order toadapt it to diverse cases and configurations without departing from theprinciples of the invention described in the following claims.

1. A method for manufacturing a multi-layered pulp-product, the methodcomprising continuously providing fibre material from at least oneentrance box of a pulp-product manufacturing machine; depositing thefibre material on at least one section of the pulp-product manufacturingmachine, thereby obtaining at least two fibre meshes that form differentlayers of the fibre material at at least one layer forming section;draining said layers during their travel along at least onelayer-forming section; introducing, by applicator means, a filler atleast between said two layers of fibre material which is being moved bya conveyor means; and joining together at least said two layers of fibrematerial, wherein the filler is selected from the group consisting ofcalcium sulphate, calcium carbonate, titanium dioxide, talc, kaolin,aluminum oxides, and combinations thereof.
 2. Method according to claim1, wherein the application means are in a variable position with respectto the formation section.
 3. Method according to claim 1, wherein thefillers are introduced by the application means on one or another layer.4. Method according to claim 1, wherein the introduction of filler isdone at a distance of 1 to 70 cm on the moving fibre mesh.
 5. Methodaccording to claim 4, wherein the introduction of filler is done at adistance of 5 to 40 cm on the moving fibre mesh.
 6. Method according toclaim 1, wherein the application means of filler are located above themoving fibre mesh and arranged in one or several series of applicationmeans at different distances from the entrance box of the pulp productmanufacturing machine.
 7. Method according to claim 6, wherein thefiller is introduced by means of one or several series of applicationmeans in successive layers.
 8. Method according to claim 1, wherein theapplication means of filler are arranged at an, angle of inclinationwith respect to the mobile fibre mesh plane comprised between 0 and 90degrees.
 9. Method according to claim 8, wherein the angle ofinclination with respect to the plane of mobile fibre mesh is comprisedbetween 0 and 45 degrees.
 10. Method according to claim 1, wherein thefiller is transferred to the mobile fibre mesh with an efficiencygreater than 70%.
 11. Method according to claim 10, wherein the filleris transferred to the mobile fibre mesh with an efficiency between 90%and 100%.
 12. Method according to claim 1, wherein the mobile fibre meshis displaced at a speed between 50 and 2000 metres per minute. 13.Method according to claim 1, wherein the introduction of filler is doneby means of spraying.
 14. Method according to claim 1, wherein thefiller is introduced as a sprayed suspension in jets of conical or planeshape with variable angles of opening.
 15. Method according to claim 14,wherein the angle of opening is 60 degrees.
 16. Method according toclaim 1, wherein the spraying of the filler is done on any of the layersof fibre material.
 17. Method according to claim 1, wherein the filleris applied prior to the joining together the layers of fibre materialwith the pulp product.
 18. Method according to claim 1, wherein theapplication means of the filler are nozzles.
 19. Method according toclaim 13, wherein the spraying is done by means of a system comprisingnozzles and a return.
 20. Method according to claim 19, wherein the flowin the nozzles is regulated by a control means and a return.
 21. Methodaccording to claim 20, wherein the flow control means in the nozzles areselected from a pressure regulator, a flow regulator and a pump equippedwith a frequency shifter. 22 Method according to claim 1, wherein thefiller penetrates inwards the moving fibre mesh with a depth that isdetermined by the distance of the application means of the filler withrespect to the entrance box of the fibre material.
 23. Method accordingto claim 1, wherein the manufacturing machine for the product is a paperor cardboard machine.
 24. Method according to claim 23, wherein thepaper or cardboard machine is selected from Fourdrinier-type machines,cylindrical machines and combinations thereof.
 25. Method according toclaim 1, wherein the filler is selected from inorganic origin, organicorigin and mixtures thereof.
 26. Method according to claim 1, whereinthe calcium carbonate is selected from a natural calcium carbonate and aprecipitated calcium carbonate.
 27. Method according to claim 1, whereinsaid calcium sulphate is an anhydrous calcium sulphate selected from:natural anhydrous calcium sulphate, anhydrous calcium sulphate comingfrom chemical synthesis, and anhydrous calcium sulphate obtained bydehydration of a calcium sulphate selected from: natural calciumsulphate hemihydrate, natural calcium sulphate dihydrate, calciumsulphate dihydrate coming from chemical synthesis, and calcium sulphatehemihydrate coming from chemical synthesis.
 28. Method according toclaim 27, wherein said calcium sulphate is dispersed in water inproportions of up to 60% by weight in relation to the total mass of thesuspension.
 29. Method according to claim 28, wherein said anhydroussulphate is dispersed by vigorous stirring.
 30. Method according toclaim 1, wherein the filler has a granulometry of between 0.5 and 50 μm.31. Method according to claim 30, characterized in that the filler has agranulometry of between 1 and 5 μm.
 32. Method according to claim 1,wherein the filler includes a dispersant in a proportion of between0.01% and 1% by weight of the dry weight of the filler.
 33. Methodaccording to claim 1, wherein the filler is applied as an aqueoussuspension consisting between 99% and 40% of water.
 34. Method accordingto claim 33, wherein the filler is applied as an aqueous suspensionconsisting between 90% and 70% of water.
 35. Method according to claim1, wherein the filler is applied controlling the flow by means of a flowregulator, by means of pressure control or by means of a flow regulatorand pressure control.
 36. Method according to claim 1, wherein thefiller applied as aqueous suspension on then fibre mesh comprisesbetween 0.5 g/m² and 50 g/m² of dry extract.
 37. Method according toclaim 36, wherein the filler applied as aqueous suspension on then fibremesh comprises between 5 g/m² and 15 g/m² of dry extract.
 38. Methodaccording to claim 36, wherein filler comprises at least one moreadditive.
 39. Method according to claim 38, wherein the filler containsdifferent types of starches or mixtures of them.
 40. Method according toclaim 24, wherein fibre material is comprised of paste selected fromamong virgin paste, recycled paste, de-inked paste, not de-inked paste,all kinds of whitened paste, all kinds of not whitened paste, andmixtures thereof.
 41. A multi-layer pulp product obtained by the methodof claim
 1. 42. A multi-layer product according to claim 41, which isselected from paper and cardboard.